The present invention relates generally to aircraft gas turbine engines, and, more specifically, to a seal for feed-through members in a firewall thereof.
An aircraft engine is mounted in an engine bay of an aircraft and includes an annular firewall surrounding the engine in the region of the combustor to separate the engine bay into a forward, relatively cool zone referred to herein as the fire zone, and a rear, relatively hot zone referred to herein as the ignition zone. Various fuel and oil lines and connections are located in the fire zone for channeling fuel into the combustor of the engine, and oil through the lubrication systems. During the useful life of the engine in the aircraft, flammable fluid such as fuel or oil may leak in the fire zone region, and the firewall is provided to reduce the possibility of the ignition thereof from the relatively hot casings contained downstream of the firewall.
The firewall typically has various feed-through members such as fluid conduits or tubes and electrical wiring harnesses which must be suitably sealed at the firewall to prevent or minimize cross fluid flow communication between the fire zone and the ignition zone during normal operation. Furthermore, the firewall must also be capable of containing any fire occurring in the fire zone for a predetermined amount of time. The typical fire test requirements as promulgated by the Federal Aviation Agency (FAA) include withstanding fire at 2,000.degree. F. (1093.degree. C.) for fifteen minutes. A new FAA Advisory Circular 20-135 has increased the stringency of the fire test requirements.
In one conventional type of firewall seal, an annular mushroom-shaped seal having a head attached to a tubular stem surrounds a feed-through member. The stem is positioned through an aperture in the firewall into the ignition zone, and the head abuts a side surface of the firewall in the fire zone to provide a seal. However, due to typical manufacturing tolerances, the feed-through member may be laterally offset from the centerline of the firewall hole, and may also be misaligned therethrough at a slight angle which decreases the ability of this type of firewall seal to effectively seal the aperture. Sufficient angular misalignment of the feed-through member may unseat a portion of the seal head which can allow an unacceptable amount of leakage between the fire and ignition zones. And, since the seal stem is exposed to the hot ignition zone, its useful life is limited.